Wojciech Szczesny says the Arsenal squad are working hard on improving the way they defend set pieces.
Arsene Wenger's side have conceded twice from corners in the opening month of the season, with Martin Demichelis' late header giving Manchester City a point at Emirates Stadium on Saturday.
Szczesny is disappointed with that statistic but insists the team are determined to put it right.
"We did very well last season on set pieces and we're a bit disappointed"
"We do realise that set pieces have been a weakness for us recently," he said. "We've conceded [a couple] of goals already and it's very early in the season.
"We did very well last season on set pieces and we're a bit disappointed. We've been working on it in training so hopefully we'll put that right on Tuesday."
Mathieu Debuchy misses the trip to Borussia Dortmund after picking up an injury at the weekend, but Szczesny is confident that the defence can cope in his absence.
"It's very disappointing to lose such an important player," he said. "He's had a very strong start to the season, he's very experienced and he's a very solid right back so we're disappointed to lose him but hopefully he'll be back as soon as possible.
"I have no difficulty playing with any of the defenders. We try to communicate in training so I don’t think that’s too much of an issue.”
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